The Two For One Overhead Special
Bill Alderson, Technology Consulting Officer, NetQoS, Inc.

Yes, it is true, when you need performance the most, during file transfers and large packet transactions your 1500 byte packets are being sliced up by VPN's and L2TP tunnels.

This results in what I call the "two for one" special...when you need it most. When you really need performance out of your VPN or Internet dialup circuit, it creates two packets (or more) for each of your packets. Not only do you increase processing overhead to create the additional packets, but it exposes your packets to twice the potential packet loss over the Internet's high packet loss environment!

The answer? Set the MTU on routers connecting to your VPN device to 1300 bytes. Then packets hitting your VPN or L2TP tunnels are ready for the additional tunnel overhead without fragmentation.